Circuit breaker is a switching device built ruggedly to enable it to interrupt/ make not just the load current but also the much larger fault current, that might occur on a circuit.
A circuit breaker holds both fixed contacts and moving contacts. The reasons of circuit breakers is to eliminate short-circuit in which occurs on a line. Circuit breakers are found at the arrivals and departures of all lines incident on a substation. Although the circuit breaker is closed these contacts are held together. The mode of action of whole circuit breakers consists in the breaking of the fault current by the separation of the moving contacts away from the fixed ones. An arc is directly established on separation of the contacts. Interruption of the current occurs after the arc at these contacts is extinguished and current becomes zero.